The present invention relates to a detector of false rotation of a power screwdriver operated by an electric motor.
Power drivers are utilized as screwdrivers in the field of precision machinery such as assembly of watches.
In screwing with power screwdrivers, the power is increased to strengthen the rotation torque when the screwdriver screws tight and can not rotate anymore. By increasing the power, the screwdriver tries to rotate, sometimes rotates a little bit and tightens the screw. The operation is called "MASHIJIME", which means final increased tightening.
The screwdriver occasionally rotates a half revolution or more in the final tightening for several reasons. One reason is that the bit of the driver rotatably slides on the screw because the bit does not match the head of the screw. Another reason is that the final tightening starts before the screw is screwed tight and the screwdriver rotating due to misoperation or a burr's stopping the rotation.
Such false rotation of the screwdriver causes very weak screwing without the final tightening, so that the device to be screwed become substandard.
In manual operation the operator may note and detect the wrong rotation of the bit. But nowadays screwdrivers are mostly operated by automatic machines like robots, which makes it difficult to detect the false rotation of the bit and causes many weak-screwed substandard devices.
An object of the invention is to provide a detector which can detect false rotation of a power screwdriver in final tightening operation.
A further object of the invention is to provide a detector which can indicate occurrence of false rotation.